With the increasing use of electromagnetic actuators for actuating final control elements, and particularly with the use of such electromagnetic actuators to actuate the gas exchange valves of piston-type internal combustion engines, the necessity arises of monitoring functional problems or failures of an actuator during operation and initiating appropriate provisions if a malfunction occurs.
According to the invention, a method is proposed for monitoring the function of an electromagnetic actuator having at least one electromagnet, which acts upon an armature, movable counter to the force of at least one restoring spring, to actuate a final control element, in particular an electromagnetic actuator for actuating a gas exchange valve of a cylinder of a piston-type internal combustion engine, in which the electrical power of the magnet is controlled via an electric controller, wherein as a monitoring parameter, the other electric power parameter, dependent on the controlled electric power parameter, is detected in its course over time as an actual value and compared with the course over time, predetermined in the controller for proper function, of the monitoring parameter as a theoretical value, and if a deviation occurs, an actuating signal is generated. In this method, the fact that the other electric power parameter, such as the voltage established at the coil, that is dependent on the controlled electric power parameter, such as the current, has significant deviations if the armature on approaching the pole face of the intercepting magnet until contact with the pole face does not perform xe2x80x9cproperlyxe2x80x9d. Since on the other hand it is possible for the course over time of the monitoring parameter, given proper function of the electromagnetic actuator, to be stored as a memorized theoretical value in the electric controller, a theoretical value for xe2x80x9cproperxe2x80x9d functioning is simultaneously made available. This theoretical value allows ongoing, uninterrupted monitoring of a single electromagnetic actuator during operation. Since deviations between the course over time of the monitoring parameter detected as the actual value from the course over time of the monitoring parameter present in the form of the theoretical value are immediately apparent in an operating situation that can be assessed as a problem, it is also possible to trip a corresponding actuating signal. The possibility then also exists of specifying a certain tolerance range, which allows further operation even if a slight deviation of the actual value from the theoretical value is ascertained. Once again, the possibility exists of initially merely detecting slight deviations and storing them in memory in their order over time and then to trip an actuating signal, for instance in the form of a display, whenever such deviations in the actual value from the theoretical value accumulate while still within the predetermined tolerance limit. The particular advantage of the method of the invention over other methods is that here problems or anomalies in operation can be detected during the entire time an electromagnetic actuator is on. Even a delayed arrival of the armature at the pole face caused for instance by increased friction, or a reverse motion of the armature without touching the pole face, or bouncing of the armature immediately after it strikes the pole face, or a premature drop of the armature if the holding current is too low, or seizing of the armature on the pole face of the electromagnet if a restoring spring breaks, can thus be detected immediately.
In one feature of the invention, it is provided that in control via the current, as the monitoring parameter, the course over time of the voltage applied to the coil is detected as the actual value and compared with the predetermined course of the voltage over time, given proper function, as the theoretical value. In this method, the fact that the course over time of the voltage has marked deviations at the coil of the electromagnet because of the induced contrary voltage is advantageously exploited if deviations in the motion of the armature are to be ascertained.
In another feature of the invention, it is provided that in control of the voltage, as the monitoring parameter, the course over time of the current flowing through the coil is detected as the actual value and is compared with the predetermined course of the current, as the theoretical value. In this design of the electric controller as well, the linkage of current and voltage by Ohm""s law results in marked deviation of the detected actual value from the predetermined theoretical value if the armature motion is not proper.
Both when the current is controlled and when the voltage is controlled, upon the approach of the armature to the pole face an additional voltage is induced, which leads to a distortion in the course over time of the electric power parameter detected as a monitoring parameter. Both in control via the current and in control via the voltage, this causes corresponding changes in the course over time of the actual value.
The further advantage of the method of the invention is that instead of the particular electric power parameters to be detected, their proportional magnitudes can also be picked up in the associated electric controller. For instance, if to control the current in the case of so-called linear current regulation the electric controller has a PID regulator, then any actual value deviations can also be picked up from the P and/or I and/or D component of the regulator.
In another feature of the invention, it is provided that in clocked control of the current, at least in the holding phase between an upper and a lower current level, for the monitoring parameter the sequence of the respective voltage rise, given proper function, of successive pulses is detected as an actual value and compared with a predetermined theoretical value of the sequence over time. This feature of the method is especially expedient whenever, because of the specification by the controller, it can be assumed with reliability that the armature will indeed come to contact the pole face of the electromagnet, and otherwise the controller is designed such that to reduce the requisite electrical energy during the holding phase, in which a reduced magnetic force is needed at the electromagnet, a reduced supply of current is effected, which furthermore is closed between two different current levels; that is, the current supply is turned off as soon as the upper current level is reached and is turned on again, when the current, because of the losses, has dropped down to a lower value again. As soon as the armature contacts the pole face, or in other words is securely held, a constant chronological order is obtained for the voltage rise each time the holding current in the clocking phase is turned on. If the armature drops during the holding phase, then because of the armature motion and the contrary voltage thus induced, a premature drop in the voltage occurs with the turnoff of the holding current, and there is a premature rise in the voltage when the holding current is turned on. If clocking is already done in the interception phase, then accordingly anomalies of motion of the armature in its approach to the pole face can be detected in same way, from deviations in the time sequence of the voltage rise and also the voltage drop in the applicable clocking. The direct evaluation of the switching signals, that is, the various on and off signals, is also advantageous.
In a feature of the invention, it is provided that if a predetermined deviation between the actual value and the theoretical value of the monitoring parameter is exceeded, the regulated electric power parameter is reregulated via the electric controller. For instance, if there is a deviation between the actual value and the theoretical value of the monitoring parameter and it is found that the armature xe2x80x9cbouncesxe2x80x9d on striking the pole face, this means that an excessively high current or voltage is being delivered to the electromagnet, so that a remedy is possible here via a suitable intervention in the electric control. If on the other hand it is found that the armature is moving but has not attained contact with the pole face, then once again the possibility exists of increasing the controlled electric power parameter accordingly via the electric controller, so as to make a greater magnetic force available.
In a further advantageous feature of the invention, in particular in an electromagnetic actuator for actuating a gas exchange valve at a cylinder of a piston engine, it is provided that is a predetermined deviation between the actual value and the theoretical value of the monitoring parameter is exceeded, the other functions at the cylinder, in particular, fuel delivery and/or ignition and/or the electromagnetic actuator for the other gas exchange valve are turned off via the electric controller. Particularly the shutoff of delivery of further quantities of fuel to the applicable cylinder assures that damage to the exhaust system, in particular the catalytic converter system, and damage from overheating of the catalytic converter. If at the same time the electromagnetic actuator turns off the other gas exchange valve at this cylinder, then both gas exchange valves remain in the open position, for instance, and thus the applicable cylinder that has been turned off runs empty and because of the absence of compression in the cylinder contents does not have a breaking effect.
Since particularly in vehicle with piston engines that are provided with an electric controller, not only the gas exchange valves, but also, as a function of the power specified by the driver via the gas pedal, the fuel quantity, instead of ignition, valve opening times, and in particular here the chronological overlaps in the opening times of the gas inlet valve and gas outlet valve, are triggered by the electric triggering, the method of the invention also offers the advantage that when the functions of a cylinder are turned off, the power of the cylinders of the piston engine that are still working is increased, within certain limits, via the electric controller. The possibility thus exists, regardless of the power specified by the gas pedal, of automatically adjusting the individual control parameters automatically, in the event of failure of only one cylinder, via a suitable control command in the electronic controller, so that the piston engine can continue to be operated with virtually the same power despite the failure of one cylinder, and a perceptible delay in vehicle speed is not brought about by a sudden power drop if one cylinder fails.